Method of producing metallic yarn



United States Patent O Int. Cl. B23p 17/00 US. Cl. 29-419 2 Claims ABSTRACT OF THE DISCLOSURE A method for producing a multifilament metallic yarn from high temperature alloys through the utilization of conventional drawing and annealing techniques. High temperature alloy wires or filaments are bundled together in a closely packed relationship and encased within an iron sheath which extends along the length of the contained wires. Simultaneously with the encasing operation, the wires are flooded with a water slurry of a finely divided inert substance selected from the group consisting of aluminum oxide, red iron oxide and boron nitride. The application of the inert substance to the filament yarn results in the coating of the individual filaments, thereby preventing metal to metal contact during a conventional drawing and annealing process. The welding together of the individual filaments during the annealing technique is thereby prevented which results in the production of a multifilament yarn possessing characteristics which make it amenable for use under high temperature conditions.

BACKGROUND OF THE INVENTION This invention relates to a multifilament metallic yarn and to a method for producing the same. More particularly, this invention concerns itself with the utilization of anti-welding agents for preventing the welding together of individual metal filaments during the fabrication of multifilament yarns from high temperature alloys.

Wire cables, filter media and protective garments are oftentimes fabricated from multifilament metallic yarn. Generally, these yarns are produced by bundling together a multitude of metal wires having a relatively small diameter. To produce such items economically, it has been found advisable to start with metal wires of a somewhat larger size than desired in the final product. After bundling the wires together, the bundle is placed in a conventional drawing die and subjected to a series of drawing operations sufficient to reduce the diameter of the individual wires to the desired dimension.

In attempting to employ multifilament metallic yarns as wire cables, filter media and protective garments for high temperature applications, it becomes necessary to manufacture the individual filaments from metal alloys possessing properties which make them suitable for use at high temperatures. The use of high temperature alloys, however, creates a fabrication problem since the wires or filaments of these alloys can be cold drawn only for nominal periods of time before in-process heat treating or annealing becomes necessary. The metal wires tend to fracture without the beneficial softening effect of the heat treatment. However, since the bundles of filaments are closely packed, there is a tendency for the wires to weld together during the heat treating step. Obviously, if the filaments are allowed to weld together they will assume the properties of a single solid strand of wire and thereby lose the desirable effects achieved from a multifilament yarn structure. To overcome this problem, each of the individual filaments of a high temperature alloy metallic yarn are subjected to an individual drawing and annealing operation. The drawing of single filaments has proved to be extremely expensive and the economies achieved by the method of first forming a bundle of wires and then subjecting the bundle to a conventional drawing operation are lost.

The utilization of the method of this invention, however, achieves the economies found in the method of first forming a bundle of wires with subsequent drawing and yet still permits the use of high temperature alloys in the fabrication of multifilaments metal yarn. A water slurry of a finely divided inert powdered substance is applied as a coating to the filaments during the bundling operation. The coating prevents metal to metal contact of the various filaments during the drawing and heating operation thus preventing the welding together of the individual metal filaments.

SUMMARY OF THE INVENTION In accordance with the present invention, it has been found that multifilament metallic yarns fabricated from high temperature or super alloys can be produced effectively and economically through the use of conventional wire drawing and annealing techniques by coating the bundles of filaments with a finely divided inert substance. The inert powder not only coats the individual fibers, but also permeates the voids between the filaments and prevents metal to metal contact between the individual filaments. The problem of filament welding during the annealing or heat treating operation is thereby eliminated.

Accordingly, the primary object of this invention is to provide a novel method for the fabrication of multifilament metallic yarns from high temperature alloys.

Another object of this invention is to provide a method for preventing the welding together of high temperature alloy filaments during the fabrication of a multifilament metallic yarn.

Still another object of this invention is to provide a method for the fabrication of multifilament metallic yarns which possess characteristics making them especially suitable for use in high temperature applications.

Still other and further objects of the present invention will become apparent upon consideration of the following detailed description thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT In practicing the present invention, it has been found that multifilament metallic yarns fabricated from high temperature alloys can be produced in an economic manner through the use of conventional wire drawing and annealing techniques. Filament yarns fabricated from high temperature alloys such as nickel and cobalt base alloys, molybdenum base alloys and stainless steel are especially useful for a variety of high temperature applications. Multifilament metallic yarns made from these alloys are fabricated by first bundling together a number of metal alloy wires or filaments in a closely packed relationship with one another. The starting bundle of metal wires is then enclosed within an iron sheath. The sheath is initially formed from a ribbon approximately .006 inch thick. It is caused to fold up around the bundle of starting strands so that the edges of the ribbon butt together forming a closed seam running parallel to the contained wire strands. The forming of the ribbon into a sheath around the bundle is accomplished by drawing these components through one or more wire drawing dies as may be required. During the sheath forming operation, the bundle of wires is flooded with a slurry comprising a mixture of about 50% by weight of a inert finely divided powdered substance selected from the group consisting of aluminum oxide, red iron oxide, and boron nitride with the balance being water. The water slurry may contain from about 20% to by weight of the inert substance, but amounts of about 50% by weight are preferable.

The slurry effectively coats the individual fibers and likewise permeates the voids between the filaments. Any excess slurry is allowed to drain away. The iron sheath containing the coated bundle is then placed in a conventional drawing die and subjected to a series of drawing and annealing steps suflicient to reduce the size of the filaments to a desired dimension. The iron sheath serves to contain the inert powdered slurry within the bundle during the yarn processing and also permits reducing all the filaments uniformly by pulling the sheathed bundle in a conventional manner through a conventional wire drawing die. The inert powder acts as an antiwelding agent and prevents the welding together of the individual filaments. The powder remains on the surface of the metal filaments during the drawing process and being in the form of a very fine powder, does not interfere with the reduction of the filaments between the drawing operations since it draws out and elongates with the metal filaments. In effect, the inert substance forms a barrier coating on the filaments so that metal to metal contact between the filaments is prevented. Welding together of the filaments is thus prevented.

As a consequence, rnultifilament metallic yarns fabricated from high temperature alloys can be produced by a bundling and drawing method that is less costly than that produced by bundling together individual filaments that have been previously drawn and reduced to the desired size. With the techniques of this invention, it has been found that as many as 100 wires of a 2-mil diameter size can be bundled together and subsequently processed to an individual filament size of about /2 mil by subjecting the bundle to conventional drawing and annealing techniques.

With the foregoing discussion in mind, there is presented herewith a detailed specific example which will illustrate to those skilled in the art the manner in which this invention is carried out. The example discloses a method for producing a stainless steel rnultifilament metal yarn through the utilization of a conventional drawing and annealing technique.

EXAMPLE 100 wires of austenitic stainless steel having an individual diameter of about 2 mils were packed together in a close relationship. The bundle of wires was then placed adjacent to a .0O6-inch iron ribbon which runs parallel along the wire bundle. The ribbon and wire bundle was then drawn through a wire drawing die in order to form an iron sheath with the wire bundle enclosed therein. During the bundling and sheathing steps, the wires were flooded with a slurry comprising an integral mixture of about 50% by weight of finely divided aluminum oxide with the balance water. Upon completion of the bundling and sheathing steps, the excess amount of the slurry mixture was allowed to drain away. The sheath encased bundle was then placed in a conventional drawing die and subjected to a series of conventional drawing operations. The bundles were drawn in succession through conventional wire drawing dies of progressively small size until the individual diameters of the wires were approximately /2 mil. At the conclusion of each drawing operation, the rnultifilament yarn was subjected to an annealing or heat treating operation at a temperature of about 2100 F. in order to soften the wires for each subsequent drawing operation.

It should be noted that the temperature of the annealing operation may be varied depending upon the alloy material and, at least in part, the severity of the successive drawing operations. The resultant metallic yarn produced from the method of the aforementioned example contained approximately one hundred filaments having individual diameters of about /2 mil in which the filaments were not welded together. Additional bundles of stainless steel filaments also were fabricated in the same manner as herein disclosed with the exception that red iron oxide powder or boron nitride powder were employed as the inert powdered substance.

From the foregoing description it will be apparent that this invention has provided a method which is most effective in producing rnultifilament yarns from high temperature alloys. Their use in the fabrication of thermal protective garments, wire cables and filter media has been found to be most advantageous in a number of high temperature operations.

The invention has been described with particular reference to specific embodiments thereof. It is to be understood, however, that the description of the present invention is for the purpose of illustration only, and it is not intended to limit the invention in any Way.

I claim:

1. A process for producing a high temperature alloy metal rnultifilament yarn which comprises the steps of preparing a bundle of closely packed high temperature filaments, encasing the said bundle within an iron sheath While simultaneously flooding said filaments with a slurry mixture consisting of about from 20% to by weight of finely divided boron nitride with the balance water, allowing any excess amount of slurry to drain away, subjecting said coated, sheathed and closely packed bundle to a series of drawing and heating operations to reduce the diameter of the individual filaments contained therein to about one-quarter of their original diameter, and then removing the sheath and finely divided boron nitride.

2. A process in accordance with claim 1, wherein the slurry mixture consists of about 50% by weight of boron nitride.

References Cited UNITED STATES PATENTS 2,050,298 8/1936 Everett. 2,718,049 9/1955 Prache. 3,394,213 7/1968 Roberts et al. 294l9 X JOHN F. CAMPBELL, Primary Examiner D. C. REILEY, Assistant Examiner US. Cl. X.R. 29423 

